Syntheses, structures and sorption properties of two framework-isomeric porous copper-coordination polymers

Abstract

Solvothermal and solution reactions of a V-shaped organic ligand 4,4′-oxybis(benzoic acid) (H₂oba) and Cu(NO₃)₂ yield two porous coordination polymers, namely [Cu(oba)(dmso)] (MCF-21) and [Cu₂(oba)₂(dmf)(C₂H₅OH)]·(dmf)₂(H₂O) (MCF-22·guest) (dmso = dimethyl sulfoxide, dmf = dimethylformamide), respectively. Single-crystal X-ray analyses reveal that the metal carboxylate backbones of MCF-21 and MCF-22·guest are framework-isomeric as two uninodal four-connected nets, i.e. a two-dimensional (2-D) 4⁴ layer and a 3-fold interpenetrated lvt (4²8⁴) three-dimensional (3-D) network, respectively. After removing the solvent molecules, MCF-21 retains a rigid 2-D framework, but MCF-22·guest exhibits either rigid or dynamic behavior depending on the degree of desolvation, which is confirmed by powder X-ray diffraction and sorption isotherms. Meanwhile, the different sorption behavior of the framework-isomeric materials is elucidated by the discrepancies of their pore dimensions and framework rigidities.